Intra-mode coding is designed for key frames, i.e., i-frames of traditional codecs, and can be regarded as a kind of image-based semantics feature compression method. Given a key frame image, that is the \(t\) -th frame \(x_t\)  of a video clip \(X\) , it is first fed into two branches in parallel. One branch employs a feature extractor module to obtain a hidden feature \(z_t\) , which is semantics-unknown and contains raw content information. The other branch leverages object parsing technique, such as CenterNet [1]}, to extract high-level semantic features from key frame \(x_t\) , which contains object spatial location information and category information. Such high-level features are not only deployed in the bitstream, but also are used to partition the encoded hidden feature \(z_t\)  into different groups (i.e., different spatial areas) \(\hat{z}_t\)  according to different categories.
